1. Field of the Invention
The present invention relates to a pickup system in an optical information recording and reproducing apparatus.
2. Background Art
Generally, when a disk is used as a information recording medium, such as a video disk, a digital audio disk, or the like, recording information signals are recorded by forming fine pits or grooves in spiral tracks on the disk surface. In the case where the thus recorded information signals are read, the tracks are irradiated with a spot of light and the changes of reflected light owing to the presence or absence of the pits are converted into electrical signals to thereby reproduce the original information signals from the electrical signals.
This reproduction requires that the light spot be exactly focused on the recording surface of the disk. Accordingly, it is necessary to perform position control (focusing servo) for an objective lens in the direction of the optical axis of the objective lens in order to focus the light spot on the recording surface. Furthermore, this reproduction requires the light spot to exactly track the recording tracks. Accordingly it is necessary to perform position control (tracking servo) for the light spot in the direction of the radius of the disk.
FIG. 1 shows an example of a previously developed pickup system.
Referring to FIG. 1, an objective lens 1 is fixedly fitted into the upper end portion of a cylindrical holder 2 and supported by a supporting mechanism 3 including the holder 2 so as to be movable in the direction of the optical axis of the objective lens, that is, the focusing direction Z, as well as in the direction perpendicular to the focusing direction, that is, the tracking direction X.
The supporting mechanism 3 is constituted by a pair of flexible springs 7, a plate-like junction member 8, and another pair of flexible springs 9. The pair of horizontally flexing springs 7 are disposed separately from each other in the tracking direction X and fixed in their portions at one end to a base 5 through brackets 4. That is, the springs 7 form cantilevers so as to be flexible in the tracking direction X. The plate-like junction member 8 is disposed between and connected at side end portions opposite to the respective free end portions of the horizontally flexing springs 7. The pair of vertically flexing springs 9 are fixed respectively at one end to the upper and lower end portions of the junction member 8 and extend to the respective fixed end side portions of the pair of horizontally flexing springs 7 so as to be connected at their other end portions, that is, their free end portions, to the outer periphery of the holder 2. The springs 9 are made flexible only in the focusing direction Z.
A round bobbin 10 is formed at the lower end portion of the holder 2 coaxially with the holder 2. A coil 11 which is wound on the outer periphery of the bobbin 10 drives the lens in the focusing direction. A pair of cylindrical bobbins 12 are provided at a center portion of the holder 2 so as to project oppositely in the tracking direction X. A coil 13 for driving the lens 1 in the tracking direction X is wound on each of the bobbins 13. The bobbin 10, and hence the coil 11, is disposed in a circular magnetic gap 16 formed in a magnetic circuit 15 fixed to the base 5. The other coils 13 are arranged so as to sandwich the holder 2 and so as to be disposed respectively in magnetic gaps 18 of a pair of magnetic circuits 17 fixed to the base 5.
Thus, the driving means for driving the objective lens 1 both in the focusing direction Z as well as in the tracking direction X is constituted by the large bobbin 10, the pair of cylindrical bobbins 12, the coil 11, the pair of coils 13, the magnetic circuit 15, the pair of magnetic circuits 17, and associated circuitry.
In the above-mentioned pickup system, the coils 11 and 13, and the magnetic circuits 15 and 17 are in the form of a stack in the focusing direction Z. Therefore, the pickup system is large in size in the focusing direction Z, causing a problem in making a compact and thin disk player. The size of the disk player is particularly important in keeping an optical information recording and reproducing apparatus compact.